cup, 4 to how many scouts you want, water, announcer
Put half a mouthfull of water in the last person’s mouth. The person should not swallow, and should not let the audience notice they have water. Have another cup filled with water for the first person.
All the people except the announcer stand in a straight line, the last person will have the water in his mouth. The anouncer will start talking about water conservation and how water is very heavy on backpacking trips and these scouts have found a way around that. The announcer turns around and asks for a demo of one of the ways to conserve water.
The first scout says ok and all start brushing their teeth with their fingers. (The last person needs to practice before hand so water doesn’t spill out.) After everybody is done “brushing” have the announcer take a cup over to the first person. Let the announcer accidentally spill some water out of the cup to show the audience there is water in there.
The first person rinses his mouth out with water and swallows the water. Then the first person will turn to the second and “transfer” water into the next scout’s ear. Repeat action down the line till last scout, who with great showmanship, spits the water out!!
Here’s an example-